Silver halide photothermographic imaging materials, often referred to as `dry silver` compositions because no liquid development is necessary to produce the final image, have been known in the art for many years. These imaging materials basically comprise a light insensitive, reducible silver source, a light sensitive material which generates silver when irradiated, and a reducing agent for the silver source. The light sensitive material is generally photographic silver halide which must be in catalytic proximity to the light insensitive silver source. Catalytic proximity is an intimate physical association of these two materials so that when silver specks or nuclei are generated by the irradiation or light exposure of the photographic silver halide, those nuclei are able to catalyze the reduction of the silver source by the reducing agent. It has been long understood that silver is a catalyst for the reduction of silver ions and the silver-generating light sensitive silver halide catalyst progenitor may be placed into catalytic proximity with the silver source in a number of different fashions, such as partial metathesis of the silver source with a halogen-containing source (e.g., U.S. Pat. No. 3,457,075), coprecipitation of the silver halide and silver source material (e g., U.S. Pat. No. 3,839,049), and any other method which intimately associates the silver halide and the silver source.
The silver source used in this area of technology is a material which contains silver ions. The earliest and still preferred source comprises silver salts of long chain carboxylic acids, usually of from 10 to 30 carbon atoms. The silver salt of behenic acid or mixtures of acids of like molecular weight have been primarily used. Salts of other organic acids or other organic materials such as silver imidazolates have been proposed, and British Pat. No. 1,110,046 discloses the use of complexes of inorganic or organic silver salts as image source materials.
In both photographic and photothermographic emulsions, exposure of the silver halide to light produces small clusters of silver atoms. The imagewise distribution of these clusters is known in the art as the latent image. This latent image generally is not visible by ordinary means and the light sensitive article must be further processed in order to produce a visual image. The visual image is produced by the catalytic reduction of silver which is in catalytic proximity to the specks of the latent image. Certain dyes can be used to spectrally sensitize photothermographic emulsions. This is accomplished by adding the dyes to the emulsion before, during, or after formation or addition of the silver halide component. See, for example, U.S. Pat. Nos. 4,461,828 and 4,476,220.
Antihalation layers are known in the photothermographic construction art. Their purpose can be to decrease light scattering by absorbance of incident and reflected light. Some antihalation agents (sometimes referred to as "acutance agents") improve image quality by reducing diffuse scattering of light from the substrate, the coated layers, or the various interfaces in a coated light-sensitive construction. Typically, they include ultraviolet light-absorbing coating surfaces, UV absorbing organic binders, and ultraviolet light-absorbing compounds and dyes, which are well known to those skilled in the art. Rutile titanium dioxide has been described as a useful antihalation agent, see for example U.S. Pat. No. 4,395,484.
Primer coatings of use in photothermographic construction typically include polyvinyl butyrals, ethyl cellulose, or polyvinyl alcohol.